Circuit breaker numbers

E_Dawg · September 5th, 2003, 13:29

Ya know those numbers on the breakers? Is that the normal amp draw of the circuts they are supposed to protect, or is the the maximum apmerees it will accept before popping?

averyrm · September 5th, 2003, 13:33

maximum before popping, I believe.

Center_Mid · September 5th, 2003, 15:40

I thought it was the normal amp load, so that if you're running on a battery you can figure out the load and do a rough amp-hour computation.

I don't know for sure - lookin' it up when I get home!

E_Dawg · September 5th, 2003, 16:30

I've been lookin' for a while and found nothing...

Hopefully you'll have better luck!

EatSleepFly · September 5th, 2003, 17:09

They are the same as fuses. The number you see on them is the maximum number of amps it can take. Any more load than that, and out it comes. (Or, in the case of a fuse...it blows).

E_Dawg · September 5th, 2003, 17:13

Cool thanks!

bluelake · September 5th, 2003, 21:46

yes, if you lose your alternator... then adding up all of the circuits that are "on" will give you the amp-hours you are using.

Unfortunately, in a LOT of older airplanes i fly in the numbers are worn off. I suspect that this is because students (and I was one of them) read the checklist "circuit breakers in" and run their fingers across it. So, its good to use the POH while sitting in your armchair to review some of the major load items... that way in flight if you lose your alternator, you'll know which ones to shed even if the numbers are rubbed off.

E_Dawg · September 5th, 2003, 22:36

It either shows the max permissible load or the normal amp load. If it's the latter you can add it up, if it's the former you can't. Anyone know for sure?

n2o2diver · September 5th, 2003, 23:25

It is the MAX AMPS before that breaker will POP, has nothing to do with how much the circuit is drawing, but you can be assured it is less than the number on the breaker.

MikeD · September 6th, 2003, 07:39

[ QUOTE ]
It is the MAX AMPS before that breaker will POP, has nothing to do with how much the circuit is drawing, but you can be assured it is less than the number on the breaker.

[/ QUOTE ]

Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw; this value varying depending on the particular circuit being protected. Breakers that regularly get pulled and reset, such as overnight shutdown, fueling, etc could actually "weaken" and pop at lower amps than advertised due to the simple fact of the breaker spring weakening from constant use. Can be a pain if you have a highly used breaker (regularly pulled) that seemingly pops for no reason, causing you to troubleshoot the associated system when the breaker itself is the real problem.

C650CPT · September 6th, 2003, 09:35

What it really is = It represents the number of times that you can reset that particular breaker.

No I'm just kidding you, it is as stated the level of protection provided to that circuit. As MikeD said the engineers figure in some additional protection for initial draws, but bigger items that have considerable draw are protected by current limiters, which are "slow blow" fuses. The current limiter protects the airplane's electrical system from shorts, once a CL is blown it cannot be reset, it must be replaced by an A&P mechanic.

aloft · September 7th, 2003, 15:08

I read the first line of that and my B.S. breaker popped.

sixpack · September 8th, 2003, 19:04

One unfortunate thing about threads, is that it's hard to undo incorrect information. (including mine, if I screw up this summary). I suspect SkyGuyEd didn't get a solid answer. Here's my summary...

[ QUOTE ]
CORRECT:
They are the same as fuses. The number you see on them is the maximum number of amps it can take. Any more load than that, and out it comes. (Or, in the case of a fuse...it blows).

INCORRECT:
yes, if you lose your alternator... then adding up all of the circuits that are "on" will give you the amp-hours you are using.

PAINFULLY CORRECT, BUT YOU CAN IGNORE THIS DETAIL:
Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw.

HUMOROUS:
What it really is = It represents the number of times that you can reset that particular breaker... ...No I'm just kidding you

[/ QUOTE ]

MikeD · September 8th, 2003, 19:11

[ QUOTE ]
One unfortunate thing about threads, is that it's hard to undo incorrect information. (including mine, if I screw up this summary). I suspect SkyGuyEd didn't get a solid answer. Here's my summary...

PAINFULLY CORRECT, BUT YOU CAN IGNORE THIS DETAIL:
Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw.

[/ QUOTE ]

But I like pain!

bluelake · September 8th, 2003, 20:10

Well now,

I dont mind at all being wrong and I also am a fan of pain, but what would be even more useful than Sixpack's play by play-slash-editorial on the accuracy of this thread's responses would be his OWN offering on what the numbers on the CB's mean

I officially change my response to this: when the alternator fails... the bigger the number.. the more soul searching ya'ought to do decide if ya' REALLY need whatever is on that circuit.

There.. hows that

sixpack · September 8th, 2003, 21:30

Now, I like that!!

September 5th, 2003, 13:29	#1
E_Dawg Moderator Join Date: Apr 2002 Location: chicago Posts: 4,232	Circuit breaker numbers Ya know those numbers on the breakers? Is that the normal amp draw of the circuts they are supposed to protect, or is the the maximum apmerees it will accept before popping?

September 5th, 2003, 13:33	#2
averyrm Old Skool Join Date: May 2002 Location: LCK Posts: 1,653	Re: Circuit breaker numbers maximum before popping, I believe.

September 5th, 2003, 15:40	#3
Center_Mid Junior Member Join Date: Jun 2003 Location: Seattle, WA Posts: 213	Re: Circuit breaker numbers I thought it was the normal amp load, so that if you're running on a battery you can figure out the load and do a rough amp-hour computation. I don't know for sure - lookin' it up when I get home!

September 5th, 2003, 16:30	#4
E_Dawg Moderator Join Date: Apr 2002 Location: chicago Posts: 4,232	Re: Circuit breaker numbers I've been lookin' for a while and found nothing... Hopefully you'll have better luck!

September 5th, 2003, 17:09	#5
EatSleepFly Old Skool Join Date: Dec 2002 Location: ?? Posts: 4,600	Re: Circuit breaker numbers They are the same as fuses. The number you see on them is the maximum number of amps it can take. Any more load than that, and out it comes. (Or, in the case of a fuse...it blows).

September 5th, 2003, 17:13	#6
E_Dawg Moderator Join Date: Apr 2002 Location: chicago Posts: 4,232	Re: Circuit breaker numbers Cool thanks!

September 5th, 2003, 21:46	#7
bluelake Senior Member Join Date: Dec 2001 Location: Redding, CA Posts: 619	Re: Circuit breaker numbers yes, if you lose your alternator... then adding up all of the circuits that are "on" will give you the amp-hours you are using. Unfortunately, in a LOT of older airplanes i fly in the numbers are worn off. I suspect that this is because students (and I was one of them) read the checklist "circuit breakers in" and run their fingers across it. So, its good to use the POH while sitting in your armchair to review some of the major load items... that way in flight if you lose your alternator, you'll know which ones to shed even if the numbers are rubbed off.

September 5th, 2003, 22:36	#8
E_Dawg Moderator Join Date: Apr 2002 Location: chicago Posts: 4,232	Re: Circuit breaker numbers It either shows the max permissible load or the normal amp load. If it's the latter you can add it up, if it's the former you can't. Anyone know for sure?

September 5th, 2003, 23:25	#9
n2o2diver Junior Member Join Date: May 2002 Location: Livin the Dream Posts: 220	Re: Circuit breaker numbers It is the MAX AMPS before that breaker will POP, has nothing to do with how much the circuit is drawing, but you can be assured it is less than the number on the breaker.

September 6th, 2003, 07:39	#10
MikeD Administrator Join Date: Feb 2003 Location: Pinal Airpark Posts: 6,897	Re: Circuit breaker numbers [ QUOTE ] It is the MAX AMPS before that breaker will POP, has nothing to do with how much the circuit is drawing, but you can be assured it is less than the number on the breaker. [/ QUOTE ] Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw; this value varying depending on the particular circuit being protected. Breakers that regularly get pulled and reset, such as overnight shutdown, fueling, etc could actually "weaken" and pop at lower amps than advertised due to the simple fact of the breaker spring weakening from constant use. Can be a pain if you have a highly used breaker (regularly pulled) that seemingly pops for no reason, causing you to troubleshoot the associated system when the breaker itself is the real problem.

September 6th, 2003, 09:35	#11
C650CPT Senior Member Join Date: May 2003 Location: Home Sweet Home! Posts: 957	Re: Circuit breaker numbers What it really is = It represents the number of times that you can reset that particular breaker. No I'm just kidding you, it is as stated the level of protection provided to that circuit. As MikeD said the engineers figure in some additional protection for initial draws, but bigger items that have considerable draw are protected by current limiters, which are "slow blow" fuses. The current limiter protects the airplane's electrical system from shorts, once a CL is blown it cannot be reset, it must be replaced by an A&P mechanic.

September 7th, 2003, 15:08	#12
aloft Old Skool Join Date: Sep 2001 Location: Inside your OODA loop Posts: 7,003	Re: Circuit breaker numbers I read the first line of that and my B.S. breaker popped.

September 8th, 2003, 19:04	#13
sixpack Junior Member Join Date: Jul 2003 Location: Portland, Oregon Posts: 277	Re: Circuit breaker numbers One unfortunate thing about threads, is that it's hard to undo incorrect information. (including mine, if I screw up this summary). I suspect SkyGuyEd didn't get a solid answer. Here's my summary... [ QUOTE ] CORRECT: They are the same as fuses. The number you see on them is the maximum number of amps it can take. Any more load than that, and out it comes. (Or, in the case of a fuse...it blows). INCORRECT: yes, if you lose your alternator... then adding up all of the circuits that are "on" will give you the amp-hours you are using. PAINFULLY CORRECT, BUT YOU CAN IGNORE THIS DETAIL: Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw. HUMOROUS: What it really is = It represents the number of times that you can reset that particular breaker... ...No I'm just kidding you [/ QUOTE ]

September 8th, 2003, 19:11	#14
MikeD Administrator Join Date: Feb 2003 Location: Pinal Airpark Posts: 6,897	Re: Circuit breaker numbers [ QUOTE ] One unfortunate thing about threads, is that it's hard to undo incorrect information. (including mine, if I screw up this summary). I suspect SkyGuyEd didn't get a solid answer. Here's my summary... PAINFULLY CORRECT, BUT YOU CAN IGNORE THIS DETAIL: Not necessarily. Most CBs are designed to pop at a load rating of nominal plus about 10% in order to compensate for the higher amperes on the initial current draw. [/ QUOTE ] But I like pain!

September 8th, 2003, 20:10	#15
bluelake Senior Member Join Date: Dec 2001 Location: Redding, CA Posts: 619	Re: Circuit breaker numbers Well now, I dont mind at all being wrong and I also am a fan of pain, but what would be even more useful than Sixpack's play by play-slash-editorial on the accuracy of this thread's responses would be his OWN offering on what the numbers on the CB's mean I officially change my response to this: when the alternator fails... the bigger the number.. the more soul searching ya'ought to do decide if ya' REALLY need whatever is on that circuit. There.. hows that

September 8th, 2003, 21:30	#16
sixpack Junior Member Join Date: Jul 2003 Location: Portland, Oregon Posts: 277	Re: Circuit breaker numbers Now, I like that!!

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